9,079 research outputs found
Inverse Low Gain Avalanche Detectors (iLGADs) for precise tracking and timing applications
Low Gain Avalanche Detector (LGAD) is the baseline sensing technology of the
recently proposed Minimum Ionizing Particle (MIP) end-cap timing detectors
(MTD) at the Atlas and CMS experiments. The current MTD sensor is designed as a
multi-pad matrix detector delivering a poor position resolution, due to the
relatively large pad area, around 1 ; and a good timing resolution,
around 20-30 ps. Besides, in his current technological incarnation, the timing
resolution of the MTD LGAD sensors is severely degraded once the MIP particle
hits the inter-pad region since the signal amplification is missing for this
region. This limitation is named as the LGAD fill-factor problem. To overcome
the fill factor problem and the poor position resolution of the MTD LGAD
sensors, a p-in-p LGAD (iLGAD) was introduced. Contrary to the conventional
LGAD, the iLGAD has a non-segmented deep p-well (the multiplication layer).
Therefore, iLGADs should ideally present a constant gain value over all the
sensitive region of the device without gain drops between the signal collecting
electrodes; in other words, iLGADs should have a 100 fill-factor by
design. In this paper, tracking and timing performance of the first iLGAD
prototypes is presented.Comment: Conference Proceedings of VCI2019, 15th Vienna Conference of
Instrumentation, February 18-22, 2019, Vienna, Austri
Local soil classification and crop suitability: Implications for the historical land use and soil management in Monti di Trapani (Sicily)
In the past, the lack of technologies (e.g. synthetic fertilizers) to overcome biophysical limitations has played a
central role in land use planning. Thus, landscape management and agronomic practices are reactions to local
knowledge and perceptions on natural resources, particularly soil. In the framework of the European research
project MEMOLA (FP7), the role of local farmers knowledge and perceptions on soil for the historical land
use through the spatial distribution of crops and the various management practices have been assessed in three
different areas of Monti di Trapani region (Sicily). The identification of the soil classification systems of farmers
and the criteria on which it is based, linked to the evaluation of the farmers\u2019 ability to identify and map the
different soil types, was a key step. Nevertheless, beyond the comparison of the ethnopedological classification
approach versus standard soil classification systems, the study also aims at understanding local soil management
and land use decisions. The applied methodology was based on an interdisciplinary approach, combining soil
science methods and participatory appraisal tools, particularly: i) semi-structured interviews; ii) soil sampling
and analysis; iii) discussion groups; and iv) a workshop with local edafologists and agronomists. A rich local
glossary of terms associated with the soil conditions and an own soil classification system have been identified in
the region. Also, a detailed soil map, including process of soil degradation and soil capability, has been generated.
This traditional soil knowledge has conditioned the management and the spatial distribution of the crops, and
therefore the configuration of the landscape, until the 1990s
Fast and accurate method for computing non-smooth solutions to constrained control problems
Introducing flexibility in the time-discretisation mesh can improve convergence and computational time when solving differential equations numerically, particularly when the solutions are discontinuous, as commonly found in control problems with constraints. State-of-the-art methods use fixed mesh schemes, which cannot achieve superlinear convergence in the presence of non-smooth solutions. In this paper, we propose using a flexible mesh in an integrated residual method. The locations of the mesh nodes are introduced as decision variables, and constraints are added to set upper and lower bounds on the size of the mesh intervals. We compare our approach to a uniform fixed mesh on a real-world satellite reorientation example. This example demonstrates that the flexible mesh enables the solver to automatically locate the discontinuities in the solution, has superlinear convergence and faster solve time
The Extreme Outer Regions of Disk Galaxies: I. Chemical Abundances of HII Regions
We present the first results of an ongoing project to investigate the
present-day chemical abundances of the extreme outer parts of galactic disks,
as probed by the emission line spectra of a new sample of HII regions. The
galaxies studied here, NGC628, NGC1058 and NGC6946, are all late-type spiral
galaxies, characterized by larger than average HI-to-optical sizes. Our deep
Halpha images have revealed the existence of recent massive star formation,
traced by HII regions, out to, and beyond, two optical radii in these galaxies
(defined by the B-band 25th magnitude isophote). Optical spectra of these
newly-discovered HII regions are used to investigate their densities,
ionization parameters, extinctions and in particular their oxygen and nitrogen
abundances. Our measurements reveal gas-phase abundances of O/H~10-15% of the
solar value, and N/O~20-25% of the solar value, at radii of 1.5-2 R25. Clear
evidence also exists for diminished dust extinction (Av~0-0.2) at large radii.
The combination of our measurements of outer disk HII region abundances with
those for inner disk HII regions published in the literature is a powerful
probe of the shape of abundance gradients over unprecedented radial baselines.
Within the limits of the current dataset, the radial abundance variations are
consistent with single log-linear relationships, although the derived slopes
can often differ considerably from those found if only inner disk HII regions
are used to define the fit. Interestingly, both the mean level of enrichment
and the ratio of N/O measured in extreme outer galactic disks are similar to
those values measured in some high redshift damped Lyman-alpha absorbers,
suggesting that outer disks at the present epoch are relatively unevolved.
(abridged)Comment: 36 pages, 10 embedded postscript files, 3 jpeg files, 7 postscript
tables; accepted for publication in the Astronomical Journal (August issue
Metal Abundances of KISS Galaxies III. Nebular Abundances for Fourteen Galaxies and the Luminosity-Metallicity Relationship for HII Galaxies
We report results from the third in a series of nebular abundance studies of
emission-line galaxies from the KPNO International Spectroscopic Survey (KISS).
Galaxies with coarse metallicity estimates of 12 + log(O/H) less than 8.2 dex
were selected for observation. Spectra of 14 galaxies, which cover the full
optical region from [OII]3727,3729 to beyond [SII]6717,6731, are presented, and
abundance ratios of N, O, Ne, S, and Ar are computed. The auroral [OIII]4363
line is detected in all 14 galaxies. Oxygen abundances determined through the
direct electron temperature T_e method confirm that the sample is metal-poor
with 7.61 <= 12 + log(O/H) <= 8.32. By using these abundances in conjunction
with other T_e-based measurements from the literature, we demonstrate that HII
galaxies and more quiescent dwarf irregular galaxies follow similar
metallicity-luminosity (L-Z) relationships. The primary difference is a
zero-point shift between the correlations such that HII galaxies are brighter
by an average of 0.8 B magnitudes at a given metallicity. This offset can be
used as evidence to argue that low-luminosity HII galaxies typically undergo
factor of two luminosity enhancements, and starbursts that elevate the
luminosities of their host galaxies by 2 to 3 magnitudes are not as common. We
also demonstrate that the inclusion of interacting galaxies can increase the
scatter in the L-Z relation and may force the observed correlation towards
lower metallicities and/or larger luminosities. This must be taken into account
when attempting to infer metal abundance evolution by comparing local L-Z
relations with ones based on higher redshift samples since the fraction of
interacting galaxies should increase with look-back time.Comment: 36 pages, 5 figures. ApJ, in pres
A 4-D dataset for validation of crystal growth in a complex three-phase material, ice cream
Four dimensional (4D, or 3D plus time) X-ray tomographic imaging of phase changes in materials is quickly becoming an accepted tool for quantifying the development of microstructures to both inform and validate models. However, most of the systems studied have been relatively simple binary compositions with only two phases. In this study we present a quantitative dataset of the phase evolution in a complex three-phase material, ice cream. The microstructure of ice cream is an important parameter in terms of sensorial perception, and therefore quantification and modelling of the evolution of the microstructure with time and temperature is key to understanding its fabrication and storage. The microstructure consists of three phases, air cells, ice crystals, and unfrozen matrix. We perform in situ synchrotron X-ray imaging of ice cream samples using in-line phase contrast tomography, housed within a purpose built cold-stage (-40 to +20oC) with finely controlled variation in specimen temperature. The size and distribution of ice crystals and air cells during programmed temperature cycling are determined using 3D quantification. The microstructural evolution of three-phase materials has many other important applications ranging from biological to structural and functional material, hence this dataset can act as a validation case for numerical investigations on faceted and non-faceted crystal growth in a range of materials
Modeling the radial abundance distribution of the transition galaxy ngc 1313
NGC 1313 is the most massive disk galaxy showing a flat radial abundance
distribution in its interstellar gas, a behavior generally observed in
magellanic and irregular galaxies. We have attempted to reproduce this flat
abundance distribution using a multiphase chemical evolution model, which has
been previously used sucessfully to depict other spiral galaxies along the
Hubble morphological sequence. We found that it is not possible to reproduce
the flat radial abundance distribution in NGC 1313, and at the same time, be
consistent with observed radial distributions of other key parameters such the
surface gas density and star formation profiles. We conclude that a more
complicated galactic evolution model including radial flows, and possibly mass
loss due to supernova explosions and winds, is necessary to explain the
apparent chemical uniformity of the disk of NGC 1313Comment: 14 paginas, 4 figures, to be published in ApJ, apri
Development of a qualitative PCR method for the Alexandrium (Dinophyceae) detection in contaminated mussels (Mytilus galloprovincialis)
Paralytic shellfish poisoning (PSP) is a syndrome caused by the consumption of shellfish contaminated with neurotoxins
produced by organisms of themarine dinoflagellate genus Alexandrium. A. minutum is the mostwidespread species responsible for PSP in theWestern Mediterranean basin. The standard monitoring of shellfish farms for the presence of harmful algae and related toxins usually requires the microscopic examination of phytoplankton populations, bioassays and toxin determination by HPLC. These procedures are time-consuming and require remarkable experience, thus limiting the number of specimens that can be analyzed by a single laboratory unit.Molecular biology techniques may be helpful in the detection of target microorganisms in field samples. In this study, we developed a qualitative PCR assay for the rapid detection of all potentially toxic species belonging to the Alexandrium genus and specifically A. minutum, in contaminated mussels. Alexandrium genus-specific primers were designed to target the 5.8S rDNA region, while an A. minutum species-specific primer was designed to bind in the ITS1 region. The assay was validated using several fixed seawater samples fromthe Mediterranean basin, which were analyzed using PCR along with standard microscopy procedures. The assay provided a rapid method for monitoring the presence of Alexandrium spp. in mussel tissues, as well as in seawater samples. The results showed that PCR is a valid, rapid alternative procedure for the detection of target phytoplankton species either in seawater or directly in mussels, where microalgae can accumulat
Radio Sources in Low-Luminosity Active Galactic Nuclei. I. VLA Detections of Compact, Flat-Spectrum Cores
We report a 0.2" resolution, 15 GHz survey of a sample of 48 low-luminosity
active galactic nuclei with the Very Large Array. Compact radio emission has
been detected in 57% (17 of 30) of LINERs and low-luminosity Seyferts, at least
15 of which have a flat to inverted radio spectrum (alpha > -0.3). The compact
radio cores are found in both type 1 (i.e. with broad Halpha) and type 2
(without broad Halpha) nuclei. The 2 cm radio power is significantly correlated
with the emission-line ([OI] lambda6300) luminosity. While the present
observations are consistent with the radio emission originating in star-forming
regions, higher resolution radio observations of 10 of the detected sources,
reported in a companion paper (Falcke et al. 2000), show that the cores are
very compact (= 10^8K) and
probably synchrotron self-absorbed, ruling out a starburst origin. Thus, our
results suggest that at least 50% of low-luminosity Seyferts and LINERs in the
sample are accretion powered, with the radio emission presumably coming from
jets or advection-dominated accretion flows. We have detected only 1 of 18
`transition' (i.e. LINER + HII) nuclei observed, indicating their radio cores
are significantly weaker than those of `pure' LINERs.Comment: To appear in the Astrophysical Journal, October 20, 200
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